1. Field of the Invention
The present invention relates to an image reading apparatus and can be applied to a scanner, for instance. The invention is intended to shorten the time required for transferring image data by transmitting captured image data to an external apparatus after compressing it.
2. Description of the Related Art
Conventionally, a scanner is connected to, for instance, a computer so that images can be processed in the computer.
Specifically, the scanner reads, at a high resolution, a two-dimensional image with a line sensor while moving it sequentially, and outputs captured image data to the computer via an interface such as SCSI (small computer system interface) or Centronics.
At this time, the scanner intermittently outputs, to the computer, image data that are output from the line sensor by using an internal line memory as a buffer memory. That is, the scanner temporarily stores image data that are output from the line sensor in the internal line memory. When the storage area of the line memory has been used up, the image data capturing by the line memory is suspended and image data stored in the line memory are output to the computer. Upon completion of the transfer of the image data that are stored in the line memory, the image data capturing by the line memory is restarted. Image data are output to the computer by repeating the above series of processes.
Incidentally, this type of scanner may be applied to a film scanner. The film scanner is used in a service of forming an electronic file by inputting images of a plurality of consecutive frames to a computer in what is called a mini-laboratory (i.e., a store in a town in which developing and fixing of photographs are performed). The film scanner is also used to form an image database; for example, as in the above case, image data are obtained by reading consecutive images and thumb nail images for indices are formed. In this type of use environments, conventional film scanners have a problem that the image data transfer takes long time.
For example, when images of a 35-mm film are read at a resolution of 3,072.times.2,048 (about 2,000 dpi) with a film scanner of the above type, captured image data will amount to about 18 MB. When those image data are transmitted at a transmission rate of, for instance, 1 MB/s, only the transmission of the image data takes about 18 seconds.
When image data of about 18 MB are processed by a computer, in the computer the image data is held in a virtual memory formed on a hard disk drive. Image data that is input from the film scanner needs to be recorded onto the hard disk drive each time.
As for the transfer of image data from the film scanner, image data are transmitted intermittently after the completion of each recording onto the hard disk drive. Therefore, in an actual transfer operation, only the transfer of image data takes more than 18 seconds.
In conventional film scanners, the transfer of image data takes long time as described above and hence it is difficult to capture image data from a plurality of consecutive frames in a short time.